Method of introducing fluid fuel into a blast furnace



&236 629 I Uw /N/ //V VE/VTORS JAGD/SH C. AGARWAL L. STEPHE/VSO/V CHARLES M. SC/ULL/ and ROBER T A fforney Feb. 22, 1966 J. c. AGARWAL ETAL METHOD OF INTRODUCING FLUID FUEL INTO A BLAST FURNACE Filed Dec. 19, 1962 United States Patent O 3,236,629 METHGD GF INTRODUCING FLUID FUEL INTO A BLAST FURNACE Eagdish C. Agarwal, Verona, Charles M. Siulli, Baldwm Borough, and Robert L. Stephenson, Prttsburgh, Pa., assignors to United States Steel Corporation, a corporation of Delaware Filed Dec. 19, 1962, Ser. No. %6,308 17 Claims. (Cl. 75-42) This application, which is a continuation-in-part of our copending application Serial No. 59,317 dated September 29, 1960 and now abandoned, relates to a method of introducng fluid fuel into a blast furnace and more particularly to injecting gaseous 'fuel through the tuyeres of the furnace. The coke charged to an iron producng blast furnace represents the largest single cost item in the operation of the furnace. Many attempts have been made to re duce the amount of coke required by njectng gaseous or liquid fuels into the bl ast furnace at the tuyere zone. However, these methods have not proved commercially satisfactory for various reasons. One drawback is that a large amount of carbon deposits occurred in the injection pipes. In an attempt to avoid such deposits the fuel was burned in the hot blast air, but ths resulted in premature combustion of the fuel in the tuyere so that the temperature of the tuyere was increased, thus causing rapid deterioration of the tuyere. When the fuel is burned in the tuyere it is completely combusted in many cases, thus resulting in extremely high temperatures. When the fuel is burned within the furnace in the presence of carbon the fuel does not completely combust, but instead produces carbon monoxide and hydrogen with a resultant temperature lower than that produced when complete combustion occurs. In some methods of injection, the air and fuel Were not properly mixed, ths resulting in ineflcient use of the fuel. Other methods failed because partial combustion of the injected fuel occurred in undesirable locations and the heat of the reaction was not sufficient to raise the temperature of the products of combustion to that of the molten products present so that there was a chilling effect that caused solidification of the molten products in the furnace.

It is therefore an object of our invention to provide an improved method of injecting fluid fuels through the tuyeres of a blast furnace which overcomes the problems of the prior art.

This and other objects will be more apparent after referring to the following specification and attached drawings, in which:

FIGURE 1 is a schematic View of a blast furnace showing the air and gas connection to the tuyeres; and

FIGURE 2 is a schematic View showing details of the gas connection to one of the tuyeres.

Referring more particularly to the drawings reference numeral 2 indicates a blast furnace having a plurality of tuyeres 4 spaced around its periphery. Air is supplied to the tuyeres from a bustle pipe or air manifold 6 which encircles the furnace. A fuel manifold 8 also encircles the furnace and Supplies fuel to each of the tuyeres. Each of the tuyeres 4 is connected to the air manifold 6 through the usual blowpipe 10, gooseneck 12 and tuyere stock 14. A tuyere cap 15 is provided on the tuyere stock 14 in line with the blowpipe 10. Gas or other fluid fuel is delivered to each tuyere 4 from manifold 8 through a flexible connection 16 having valves 18 and 20 therein. The gaseous fuel may be natural gas, coke oven gas or pulverized coal carried in a gas in the usual manner. The carrier gas use-d may be air, natural gas, carbon monoxide, carbon dioxide, steam or the like. When air is used it must be a very minor proportion of the amount needed for combustion. The amount used should be between 1 and 5% of the amount necessary for combustion and it is preferred to keep the amount as low as possible, since if the fuel is not substantially free of combustion air burning of the fuel will not take place as desired. Any amount over 5% will be detrimental and could result in premature burning. Oil and tar may also be injected through the apparatus described above. It will be understood that the portions of the connection 16 containing valves 18 and 20 will preferably be made of steel pipe, it only being necessary that the connection 16 be flexible over a portion of its entire length. The valve 18 is controlled by a positive flow indicator 22 which closes the valve 18 if the fuel flow from the manifold 8 is disrupted for any reason, thus preventing hot furnace gases from hacking up into the supply mani'fold 8. The valve 20 is a manual shut-oli valve which is used to stop the flow of fuel if it becomes necessary to repair or replace the tuyere or injection apparatus. The conduit 16 is connected to an injection pipe 24 by means of a coupling 26. Gate valves 28 and 30 are provided in the injection tube 24. The tube 24 passes through an opening 32 in the tuyere cap 15. A sleeve 34 having internal threads is welded to the tuyere cap 15 in alignment with opening 32. The injection tube 24 is provided with external threads 36 matching the threads of sleeve 34. A scale 38 is welded to the tuyere cap 15 with positioning lugs 40 and 42 being provided thereon, the distance between lugs 40 and 42 being equal to the critical positioning range of the tube 24. The injection tube 24 has a pointer 44 welded thereto for a purpose which will appear later. A peep sight 46 is preferably provided in the tuyere cap 15. The furnace end of the injection tube 24 terminates from the :furnace end of the tuyere 4 a distance of between /3 and 1 /3 times the internal diameter of the nose of the tuyere. The minimum distance of the injection tube from the end of the tuyere should be two inches.

To assemble the tube 24, it is threaded through the coupling 34 until the pointer 44 is opposite lug 40. In this position the furnace end of the tube 24 is located a distance from the end of the tuyere equal to 1 /3 times the internal diameter of the nose of the tuyere. To adjust the position of the injection tube 24, flow of fuel to the tuyere is stopped by closing valve 20 and valve 28 is closed to prevent the furnace gases from passing through the injection tube 24. The connection between the injection tube 24 and fleXible conduit 16 is then broken at union 26 and the injection tube 24 threaded further through sleeve 34 into the tuyere 4 until the pointer 44 is opposite the desircd point on scale 38. The union 26 is then connected and fuel flow restored by opening valves 20 and 28. If the injection pipe 24 should become obstructed valves 28 and 30 may be opened to pcrmit cleaning out of the injection pipe by means of a rod.

In one specific example of our invention natural gas at the rate of approximately 4% of the air blast was injected into the tuyeres of the furnace. The injection tubes 24 were positioned with their ends terminating at a point two inches from the furnace ends of the tuyeres. The air blast velocity was maintained at 950 ft. per second at the discharge end. of the tuyeres and the velocity of the natural gas was maintained at 2250 ft. per second through the injection tubes so as to give a velocity ratio of 1 to 4.25. The pressure drop in the injection tube was 2.35 lbs. per sq. inch. We have found that the velocity of gaseous fuel through the injection tube must be a minimum of 200 ft. per second, prefarbly between 200 and 400 ft. per second. We have also found that for best results the velocity of the gaseous fuel at the nose of the tuyere should be between 20% and of the air velocity at the nose of the tuyere. Also, the gaseous fuel Volume should be between 1% and 8% of the air blast Volume.

For both liquid and gaseous fuels the pressure drop in the injection tube 24 should be between 1 and 4 lbs. per sq. inch and the location of the furnace end of the injection tube must be as described above.

In some cases oxygen may be injected to take the place of some of the air delivered through the blow pipe 10. Regardless of whether the combustion oxygen is provided entirely by the air blast or partially by injected oxygen, the total amount of oxygen supplied is substantially greater than the oxygen required for burning the fluid fuel to carbon monoxide and hydrogen. The total amount of oxygen supplied will be at least twice that required to so burn the fluid fuel in the presence of coke (carbon) in the furnace.

While one embodiment of our invention has been shown and described it will be apparent that other adaptations and modifications may be made without departing from the scope of the following claims.

We claim:

1. The method of Operating a blast furnace containing molten metal and coke, said blast furnace having a plurality of tuyeres each connected to a manifold through a blowpipe, which method comprises introducing air into each tuyere, inserting an injection tube through each of said blowpipes into the associated tuyere until the discharge end of the injection tube is at a distance from the discharge end of the tuyere equal to between /3 and 1 /3 times the internal diameter of the nose of the tuyere, and introducing fluid fuel substantially free of combustion air into said injection tubes, the amount of air in the fuel not exceeding of the air necessary for combustion.

2. The method of Operating a blast furnace containing molten metal and coke, said blast furnace having a plurality of tuyeres each connected to a manifold through a blowpipe, which method comprises introducing air into each tuyere, inserting an injection tube through each of said blowpipes into the associated tuyere until the discharge end of the injection tube is at a distance from the discharge end of the tuyere equal to between /3 and 1 /3 times the internal diameter of the nose of the tuyere, and introducing fuel gas substantially free of combustion air into said injection tubes at a velocity of at least 200 feet per second with the velocity of the fuel gas at the nose of the tuyere being beween and 100% of the air velocity, the amount of air in the fuel not exceeding 5% of the air necessary for combustion.

3. The method of Operating a blast furnace according to claim 2 in which the pressure drop in each injection tube is at least 1 pound per square inch.

4. The method of Operating a blast furnace containing molten metal and coke, said blast furnace having a plurality of tuyeres each connected to a manifold through a blowpipe, which method comprises introducing air into each tuyere, inserting an injection tube through each of said blowpipes into the associated tuyere until the discharge end of the injection tube is at a distance from the discharge end of the tuyere equal to between /3 and 1 /3 times the internal diameter of the nose of the tuyere, and introducing fuel gas substantially free of combustion air into said injection tubes at a velocity of between 200 and 400 feet per second with the velocity of the fuel gas at the nose of the tuyeres being between 20% and 100% of the air velocity, the amount of air in the fuel not exceeding 5% of the air necessary for combustion.

5. The method of Operating a blast furnace according to claim 4 in which the pressure drop in the injection tubes is between 1 and 4 pounds per square inch.

6. The method of Operating an iron producing blast furnace containing molten metal and coke, said blast furnace having a plurality of tuyeres each connected to a manifold through a blowpipe, which method comprises introducing air into each tuyere, inserting an injection tube through each of said blowpipes into the associated tuyere until the discharge end of the injection tube is at a distance from the discharge end of the tuyere equal to between /3 and 1 /3 times the internal diameter of the nose of the tuyere, and introducing fuel gas substantially free of combustion air into said injection tubes in an amount between 1% and 8% of the air blast Volume, the amount of air in the fuel not exceeding 5% of the air necessary for combustion.

7. The method of Operating a blast furnace according to claim 6 in which the pressure drop in each injection tube is at least 1 pound per square inch.

8. The method of Operating an iron producing blast furnace containing -molten metal and coke, said blast furnace having a plurality of tuyeres each connected to a manifold through a blowpipe, which method comprises introducing air into each tuyere, inserting an injection tube through each of said blowpipes into the associated tuyere until the discharge end of the injection tube is at a distance from the discharge end of the tuyere equal to between /3 and 1 /3 times the internal diameter of the nose of the tuyere, introducing fuel gas substantially free of combustion air into said injection tubes in an amount between 1% and 8% of the air blast Volume and at a velocity of at least 200 feet per second with the velocity of the fuel gas at the nose of the tuyeres being between 20% and of the air velocity, the amount of air in the fuel not exceeding 5% of the air necessary for combuston,

9. The method of Operating a blast furnace according to claim 8 in which the pressure drop in each injection tube is at least 1 pound per square inch.

10. The method of Operating a blast furnace accordng to claim 8 in which the velocity of the fuel gas is between 200 and 400 feet per second.

11. The method of Operating a blast furnace according to claim 10 in which the pressure drop in the injecton tubes is between 1 and 4 pounds per square inch.

12. The method of Operating an iron producing blast furnace containing molten metal and coke, said blast furnace having a plurality of tuyeres each connected to a manifold through a blowpipe, which method comprises ntroducing into the furnace a fluid fuel and suflicient oxygen to burn the fluid fuel and combine with the coke, at least a portion of said oxygen being introduced as heated air through the blowpipe to each tuyere, the total amount of oxygen being at least twice the amount necessary to burn the fluid fuel to carbon monoxide and hydrogen, inserting an injection tube through each of said blowpipes into the associated tuyere until the discharge end of the injection tube is at a distance from the discharge end of the tuyere equal to between /3 and 1 /3 times the internal diameter of the nose of the tuyere, and ntroducing the fluid fuel susbtantially free of combustion ar nto said injection tubes, the amount of air in the fuel not exceeding 5% of the air necessary for combustion.

13. The method of Operating a blast furnace according to claim 12 in which the pressure drop in each injection tube is at least 1 pound per square inch.

14. The method of Operating a blast furnace according to claim 12 in which the fluid fuel is gaseous and its velocty n the injection tubes is at least 200 feet per second with the velocity of the fuel gas at the nose of the tuyeres being between 20% and 100% of the air velocity.

15. The method of Operating a blast furnace according to clam 14 in which the pressure drop in each injection tube lS at least 1 pound per square inch.

16. The 'method of Operating a blast furnace according to claim 12 in which the fluid fuel is gaseous and its velocity is between 200 and 400 feet per second.

17. The method of Operating a blast furnace according to claim 16 in which the pressure drop in the injection tubes is between 1 and 4 pounds per square inch.

(References on following page) References Csted by the Examiner UNITED STATES PATENTS FOREIGN PATENTS &84,493 12/1961 GreatBritain.

%%i 5 OTHER REFERENCES Muguet 75 42 E. R. Dean: "Utilzation of Fuel Gas by Injecton Pomykala 266-29 Through Gas Furnace Tuyeres, Blast Furnace and Steel Wagner 266-39 Plant, May 1961, pages 417-422.

Toulmin 75-41 Cuscoleca 75-41 10 DAVID L. RECK, Primary Exam'ner.

Sanders 75-42 

1. THE METHOD OF OPERATING A BLAST FURNACE CONTAINING MOLTEN METAL AND COKE, SAID BLAST FURNACE HAVING A PLURALITY OF TUYERES EACH CONNECTED TO A MANIFOLD THROUGH A BLOWPIPE, WHICH METHOD COMPRISES INTRODUCING AIR INTO EACH TUYERE, INSERTING AN INJECTION TUBE THROUGH EACH OF SAID BLOWPIPES INTO THE ASSOCIATED TUYERE UNTIL THE DISCHARGE END OF THE INJECTION TUBE IS AT A DISTANCE FROM THE DISCHARGE END OF THE TUYERE EQUAL TO BETWEEN 1/3 AND 1 1/3 TIMES THE INTERNAL DIAMETER OF THE NOSE OF THE TUYERE, AND INTRODUCING FLUID FUEL SUBSTANTIALLY FREE OF COMBUSTION AIR INTO SAID INJECTION TUBES, THE AMOUNT OF AIR IN THE FUEL NOT EXCEEDING 5% OF THE AIR NECESSARY FOR COMBUSTION. 